1. Field of the Invention
This invention relates to a twist drill for drilling, a drill with a cutting insert, and a replaceable cutting insert for a twist drill.
This invention also relates to a drill with a replaceable cutting insert, whereby the cutting insert sits in a receptacle that runs through the base body at a right angle to its longitudinal axis and opens toward the drill tip, and whereby the cutting insert is in contact with the side walls of the receptacle with two essentially diametrically opposite contact surfaces.
2. Background Information
The modern metalworking trade primarily uses twist drills to make borings. Depending on the application, these twist drills can differ in terms of their cutting material and geometry. The high-speed tool steel (HSS) traditionally used is increasingly being replaced by carbide metal, which has a significantly higher resistance to abrasion. For large drilling tools, however, a drill made entirely of solid carbide metal is generally too expensive, and is not economical in spite of its excellent cutting performance. Alternatives are twist drills in which a drill tip made of carbide metal is soldered into a carrier tool which is generally made of tool steel. The disadvantage of these tools, however, is that they can be repainted only to a restricted extent. As soon as the short cutting portion made of cemented carbide metal has been used up, the entire tool has to be scrapped.
European Patent No. 441 302 A1, German Patent No. 196 05 157 A1 and U.S. Pat. No. 5,649,794 describe twist drills in which the tool tip is connected to the base body of the drill with small screws. Compared to the twist drills described above, however, these tools, which are also called “tip cutters”, generally have the disadvantage that their stability is reduced on account of the borings that are countersunk into them for the screws. These threaded connections can also interfere with the chip flow. The screws also restrict the potential applications of such drilling tools for small diameter borings. In practice, screws smaller than M2 can no longer be handled on an industrial scale. The prior art also describes drilling tools in which the cutting bodies are held in the carrier tool only by a press-fit (see, for example, German Patent No. 44 35 857 A1 or European Patent No. 460 237 A1). With a solution of that type, however, there is no way to prevent the cutting bodies from coming detached when the drill is extracted from the boring. Such tools are therefore very difficult to use in automated fabrication operations. WO 98/10881 A1 also discloses tools in which the drill tips are connected with the base body in the manner of a bayonet connection. On these drilling tools, of course, the cutting body does not come detached from the base body of the drill when the drill is extracted from the boring, but they are relatively expensive to manufacture.